Research On The Key Technologies Of Heterogeneous Networks In Future Wireless Networks

In the recent years, the wireless industry has been preparing for the emerging fifth-generation (5G) standards. A 5G system is featured by (1)addressing the demands and business contexts of 2020 and beyond, (2)creating an access network to enable a fully mobile and interconnected society, (3) providing massive amount of miscellaneous devices with the connections to packet data network, and (4) bearing huge volume of data services in the manner of a deeply heterogeneous system. 5G achieves higher speed, increased capacity, decreased latency, and better quality of service (QoS). Although HetNets can provide seamless coverage and high performance, the commercial application is challenged by the large volume of data traffic and the limitation of resources caused by high density of small cells. Meanwhile, the developing scale of HetNets induces an explosive growing volume of mobile data traffic which leads to critical inter-tier interference.The rapidly evolved and diversified market demands have imposed a huge challenge to the conventional mobile broadband network architecture.On one hand, the limited space of machine room and insufficient power supply make it impossible to accommodate the exponentially growing network equipment of operators. On the other hand, net heterogeneity caused by different specifications of wireless access equipment brings about costly troubles on management and optimization. This dessertation,correspondingly, reviews a holistic solution involving different technologies, i.e., network function virtualization (NFV), software defined network (SDN) and heterogeneous cloud radio access network (H-CRAN).In particular, I investigate both existing standards and possible extensions for 4G/5G mobile networks, followed by a few open issues for future research.After the research on the future network intelligent architecture, I focus on the following 3 innovation aspects in this dissertation.1) Spectrum sensing and management for HetNetsIn this dessertation, I focus on spectrum sharing in heterogeneous networks (HetNets) and consider Stackelberg game exploiting the cognitive radio (CR) technology to utilize those scarce resources. In the game, the licensed network controls and prices the available spectrum resource which the LPN can pur-chase and use to serve the attached user nodes as well as offload some nodes in licensed network. Both kinds of nodes try to maximize their own utility which is consisted of data rates,earning and expenditures on spectrum trading. During the dynamic interaction of the game, the interference coor-dination features of the HetNet and CR technology are employed so that the change of spectrum allocation can be fully exploited. According to simulation result, we evaluate the impact on throughput performance after implementing proposed game strategy in the HetNet. And we prove that the proposed approach can significantly improve the throughput of victim licensed nodes with slightly decreasing network total throughput.There are limited radio resources of mobile cellular network, thus making the system with high efficiency is becoming especially important.In proposed solution, we use optimization algorithm make the system becomes more efficient in dealing with nonlinear complex problem. Due to the update of highly software-oriented system, it is quite cost effective using NFV and SDN architecture. It is proved that the proposed scheme is beneficial helps the system to be more scalable, flexible and intelligent.2) Multi-user MIMO sensing and scheduling for HetNetsDifferent from previous works, this dessertation develops a cognitive MU-MIMO scheduling scheme by taking into account circular array, inter-cell interference coordination and codebook optimization. It is considered with the following features: (i) macrocells and small cells interfere with each other since they share the same spectrum, (ii) the LPNs apply circular array and sense the interference and users by different angle directions, (iii)users are grouped according to their channel status and scheduled based on codebooks. Simulation results and the analysis demonstrate that the proposed schemes can significantly improve the system throughput and user rate, with increased SINR of the whole system.3) Massive MIMO precoding schemes for HetNetsConventional MIMO precoding schemes usually perform in the baseband domain and utilize a fully digital precoder, modifying both the amplitude and phase of transmitted signals. Although a fully digital precoding scheme usually brings optimal performance, enormous hardware complexity and energy consumption become serious problems because of the expensive radio frequency (RF) chain for each antenna. This becomes a serious problem due to the huge amount of antennas at the massive MIMO transmitter side. Fortunately, the hybrid precoding scheme that combines digital precoding and analog precoding together has been proposed to significantly decrease the number of RF chains, which is considered to be an essential technique for realistic 5G MIMO systems. In this work, we presented the flexible and scalable 5G H-CRAN architecture and focused on RRM and interference mitigation massive MIMO precoding scheme. Furthermore, we proposed a null-space based hybrid precoding scheme with a flexible CSI acquisition process. By performing precoding within the null-space of the neighboring victim users, the proposed scheme counteracted the interference impact that could result in degradation of performance. Performance evaluation showed that the proposed design could acquire higher system throughput with a large amount of transmitting antennas and was capable of sufficient SE comparing with other outstanding precoding schemes.This dissertation focuses on the key technologies in future HetNets and makes outstanding improvements on the system performance.